1. Field of the Invention
The present invention is generally concerned with ultraviolet radiation drying ovens of the type used when the product to be dried is a synthetic product which must be polymerized to dry it.
It is more particularly directed, but not necessarily exclusively so, to the situation in which a drying oven of the above kind is designed to be fitted to a printing machine including a turret which is mounted to rotate about its axis and which carries, radially, at its periphery, a plurality of object-carrier supports which are themselves mounted to rotate on the turret, and at least one workstation which is fixed and past which the object-carrier supports move.
2. Description of the Prior Art
When, as is usually the case, the object to be treated must be printed several times in succession with different colors, a plurality of workstations is in practice circumferentially distributed around the axis of the turret; most of them are printing stations, although the first one can be a varnishing station, with at least one drying oven downstream of each workstation in the direction of rotation of the turret.
If the drying oven is an ultraviolet radiation drying oven, it usually includes a chamber containing the necessary lamp with a localized opening, through which the radiation passes, in line with the path of the object-carrier supports.
With an ultraviolet radiation drying oven of the above kind the problem arises of confining the radiation within the corresponding chamber.
Otherwise, this radiation could affect the operation of the adjacent workstation, causing premature and therefore untimely polymerization of the product used at that station.
This is the case in particular if a workstation is a screenprinting station.
If unintended ultraviolet radiation reaches a printing station of this kind, there is the risk of the mesh of the corresponding screen becoming progressively clogged.
To alleviate this drawback, it has been proposed to add a cover to the drying oven which, extending laterally on either side of the drying oven, forms a kind of corridor for the object-carrier supports, along which the object-carrier supports move before reaching the drying oven and after leaving it.
There is therefore always at least one object-carrier support between the chamber of the drying oven and the entry and exit of the corridor and this intercepts the corresponding radiation and prevents it being propagated to the outside.
However, the footprint of a cover of the above kind on the working area of the machine is large, which is to the detriment of its capacity in terms of workstations.
It has also been proposed to associate with the opening in the chamber of an ultraviolet radiation drying oven of the above kind a mask mounted to move between a closed position in which it interferes with the opening and an open position in which it exposes it.
Apart from the fact that prior art implementations of this kind are generally bulky at the present time, they are all always relatively complex and are not totally effective.
At present there usually remains a transient period during which, having to move from its closed position to its open position to allow an object-carrier support to pass it, the mask allows the radiation it has to intercept to filter out, at least momentarily.
A general object of the present invention is an arrangement which avoids these drawbacks.
To be more precise, the invention consists in an ultraviolet radiation drying oven including a chamber containing the necessary lamp and which has a localized opening for the radiation to pass through and, associated with the opening, a mask mounted to move between a closed position in which it interferes with the opening and an open position in which it exposes it, in which oven the mask is mounted to rotate relative to the chamber, is divided into two shutters in diametrally opposite positions and is associated with a second mask which is also divided into two shutters, is coaxial with the first mask and, like the first mask, is mounted to rotate relative to the chamber with a motion that is the converse of that of the first mask.
Because of the features of the invention, the footprint of the drying oven on the working area of the machine to which it is fitted is hardly greater than that of an object-carrier support, since it is sufficient for the rotary masks that it includes, in accordance with the invention, to be able to closely surround an object-carrier support of this kind.
The capacity of the machine, in terms of the number of workstations, can advantageously be increased commensurately.
Furthermore, because of the simultaneous use of two masks operating in opposite directions, propagation of radiation to the outside is prevented at all times, without any transient period during which radiation could escape.
The features and advantages of the invention will emerge from the following description which is given by way of example and with reference to the accompanying diagrammatic drawings.